Although many methods for atmospheric pressure ionization are known, methods as DART (Direct Analysis in Real Time) (Registered U.S. Trademark) or DESI (Desorption Electrospray Ionization) is recently drawing attention (see Patent Document 1).
DART is a method that adds protons (being generated by Penning ionization of atoms or molecules in which atoms or molecules of an electronic excited state collide with water in the atmosphere) to a sample and ionizes the sample. For example, in a case of using helium (He (23S) of a metastable excited state, a sample M can be ionized by performing the following.He(23S))+H2O→H2O+*+He(11S)+e−H2O+*+H2O→H3O++OH*H3O++nH2O→[(H2O)nH]+[(H2O)nH]++M→MH++nH2O
Here, “He(23S)” indicates helium of a triplet metastable excited state, “H2O+*” indicates a radical of H2O, and “MH+” is an example of an object ionized by adding protons to a sample.
DESI is a method that adheres an ionized solution to a sample and desorbs ions.
When measuring a sample by using DART or DESI, there is a case where a mass spectrometer is to be calibrated by using a calibration reagent. Further, when detecting a position of a chemical substance while moving a sample to which the chemical substance is adhered by using DART or DESI, there is a case where a reference position cannot be arbitrarily set.